Absorbent gelling materials (AGM's) are polymeric materials which are capable of absorbing large quantities of fluids such as body fluids and wastes and which are further capable of retaining such absorbed fluids under moderate pressures. These absorption characteristics of absorbent gelling materials make such materials especially useful for incorporation into absorbent articles such as disposable diapers, incontinent pads and catamenial napkins. For example, Procter & Gamble; European patent application No. EP-A-122,042; published Oct. 17, 1984 discloses absorbent structures wherein discrete particles of absorbent gelling material (hydrogel particles) are dispersed in a web of hydrophillic fibers. Additionally, U.S. patent application Ser. No. 734,426 filed on May 15, 1985 by Paul T. Weisman, Dawn I. Houghton and Dale A. Gellert discloses an absorbent article having a dual-layer absorbent core wherein a shaped core component consists essentially of hydrophillic fiber material and an insert core component consists essentially of a substantially uniform combination of hydrophillic fiber material and discrete particles of absorbent gelling material.
However, several difficulties have been encountered in airlaying absorbent cores having a multiplicity of layers and/or layers containing a mixture of fibers and particular amounts of discrete particles of materials such as absorbent gelling materials. Airlaying apparatus and methods require the removal of the gas or air which transports the fiber/particle admixture from beneath the foraminous forming element of the airlaying apparatus. During this removal, small particles which are mixed with the fibers can generally be drawn along with the air through the voids in the foraminous forming element, resulting in a loss of expensive absorbent gelling materials through the airlaying apparatus, the resultant absorbent article also having a reduced quantity of absorbent gelling material dispersed throughout its absorbent core resulting in a loss of absorbent capacity in the articles. Additionally, relatively large particles tend to plug or block the flow of air through the foraminous forming element resulting in a loss of uniformity of basis weight across or along the fibrous web or absorbent core as well as machinery down time necessitated in order to unplug the foraminous forming element. Thus, it would be advantageous to provide apparatus for and methods of airlaying fibrous webs having discrete particles of material, such as absorbent gelling materials, dispersed through at least a portion of the web wherein the apparatus and methods minimize plugging problems as well as the loss of materials through the foraminous forming element. It would also be advantageous to provide apparatus for and methods of forming airlaid fibrous webs having a multiplicity of layers.
The present invention provides a solution in which a dusting layer of hydrophillic fibers is deposited on the foraminous forming element prior to depositing the admixture of hydrophillic fibers and discrete particles of absorbent gelling material. This solution requires the use of two deposition chutes and hoods disposed around the periphery of the laydown drum. It has been discovered that as the laydown drum rotates from the dusting layer deposition chute to the first deposition chute, the chute configurations, the fiber/air velocities, the pressure differential along the edge of the dusting layer and the impingement of the fiber/particle admixture on the dusting layer are contributing factors in causing the dusting layer to shear or disperse resulting in an increase in plugging and loss of the particles of absorbent gelling material. Thus, it is also desired to provide an airlaying apparatus in which a dusting layer can be airlaid onto the foraminous forming element and have a primary layer airlaid over the dusting layer without damaging or destroying the dusting layer.
Accordingy, it is an object of the present invention to provide an apparatus for and method of airlaying fibrous webs having discrete particles dispersed through at least a portion of the web.
It is another object of the present invention to provide an apparatus for and method of airlaying fibrous webs having a multiplicity of layers.
It is a further object of the present invention to provide apparatus and methods which minimize equipment plugging problems as well as the loss of particles through the apparatus.
It is also an object of the present invention to provide an apparatus wherein a dusting layer is not damaged or destroyed when additional fibers or fiber/particle admixtures are airlaid over the dusting layer.